1. Field of the Invention
The present invention relates to the adjustment of friction torque devices such as clutches for motors of vehicles and the like. The present invention provides, among other things, a novel method and apparatus for pre-setting a self-adjusting clutch and, in particular, for pre-setting a self-adjusting clutch manufactured by Dana Corporation's Spicer Clutch Division of Auburn, Indiana known as the Spicer Solo, Adjustment-Free Clutch (the "Spicer Clutch").
2. Background of the Invention
Self-adjusting clutches like the Spicer Clutch allow clutches to be operated throughout their life without "manual clutch adjustments" that common clutches require. Otherwise, for example, thirteen or more manual clutch adjustments may be needed. A greater clutch life is also available with such self-adjusting clutches.
Self-adjusting clutches like the Spicer Clutch could not previously be set to sufficiently small tolerances for a number of applications. Specifically, manufacturers and service departments could only set the release bearing to within about 0.100 of an inch. This degree of inaccuracy, i.e., tolerance, for the initial setting of such self-adjusting clutches has proven to be problematic and disadvantageous. For example, a smaller tolerance of about 0.06 inches is needed for trucks by Mack Trucks, Inc.
This inability to provide sufficiently small tolerances has created an industry-wide problem. It has also added costs to trucks, delayed deliveries, and frustrated both internal and external customers. This inability to pre-set the initial setting within a sufficient tolerance range has substantially compromised the benefits, life-expectancy, and operation of such self-adjusting clutches.
Among other things, a variation in the clutch position creates a corresponding variation in the pedal position in the vehicle. Typically, with vehicles of Mack Trucks, Inc. for example, the ratio of clutch/pedal movement is about (0.010 inches at the clutch)/(0.136 inches at the pedal). A tolerance range of 0.100 thus allows a variation of about 1.36 inches at the vehicle pedal. As a result, a variety of problems can occur. For example, proper operation of a clutch brake can be disturbed which can result in damage or wear, the vehicle operator's normal clutch operation can be disturbed (e.g., removing typical play in the pedal), and other problems can occur.
There is thus a substantial need in the art for a method and/or apparatus that can improve the pre-setting accuracy of self-adjusting clutches such as a Spicer Clutch.
FIGS. 1-3 illustrate an exemplary self-adjusting Spicer Clutch in an assembled condition on a vehicle--i.e., after the engine and the transmission have been connected. These FIGS. are included as a brief explanatory background and are incorporated from U.S. Pat. No. 5,595,274. The entire disclosure of the '274 patent is, however, incorporated herein by reference.
FIG. 1 shows a clutch 20 that selectively transmits torque from an engine flywheel 22 to a driven shaft 24 of a vehicle transmission 26. A standard clutch release assembly 28, operated via a pedal 30, is used for disengaging the clutch from the flywheel 22. The flywheel 22 is fixed to a cover 32 and rotates therewith. A pressure plate 34 and a driven member 36 that is fixed to the driven shaft 24 are sandwiched between the flywheel 22 and the cover 32. The pressure plate 34 is selectively moved to the left to transmit torque from the flywheel 22 to the driven shaft 24 via the friction pads 38.
When the friction pads wear, an adjustment mechanism 42 automatically adjusts the clutch to compensate for this wear. The adjustment mechanism 42 includes an adjusting ring 44, a left cam ring 46 secured to adjusting ring 44, and a right cam ring 48.
Coil springs 56 interposed between the cover 32 and a retainer 54 urge the retainer 54 to the left. A plurality of levers 58 are radially interposed between the retainer 54 and the adjustment mechanism 42. As a result, leftward movement of the retainer assembly 28 causes the levers 58 to apply a leftward force on the pressure plate to engage the clutch members.
The left cam ring 46 is fixedly secured to the adjusting ring 44 which is rotatably fixed to the cover 32 but which is permitted limited axial movement. In contrast, the right cam ring 48 is permitted limited rotational movement with respect to the cover 32. The right face of the left cam ring 46 includes a plurality of annular ramps 80 around the perimeter thereof. Similarly, the left face of the right cam ring 48 has a plurality of like annular ramps, while the right face of the right cam ring 48 contacts the cover 32. The ramps of the right cam ring 48 cam against the ramps 80 of left cam ring 46. The surfaces of the ramps also include serrations, or teeth, which assist in locking the contacting surfaces together and which increase the frictional resistance between the cam rings.
An indicator tab 106 extends from the right cam ring 48 through a circumferential slot 108 in the cover 32. The indicator tab 106 indicates the amount that right cam ring 48 has rotated with respect to the cover 32 and, thus, the amount of adjustment which has occurred within the clutch 20.
A spring assembly (not shown) biases the right cam ring 48 to rotate with respect to cover 32. When under tension, the spring assembly biases the right cam ring to rotate with respect to the left cam ring under conditions required for adjustment. As the right cam ring 48 rotates clockwise, the ramps cam against each other, moving the adjusting ring 44 from a first axial position to a second axial position, increasing the axial displacement of the left cam ring and the right cam ring.
When the clutch 20 is fully disengaged, the pull assembly 52 of the release assembly 28 contacts the transmission housing 55, which is the extreme right position for release assembly 28, as shown in FIG. 3. The radially outer portion of the lever 58 leverages the adjusting ring away from the cover 32 and creates a gap between the left and right cam rings. The biasing forces on the right cam ring 48 caused by the spring assembly rotate the right cam ring 48. This, in turn, results in camming along ramps 80 and 88 to increase the axial displacement of adjustment mechanism 42 to fill the gap. This action repeats each time wear has occurred on friction surface 40 and when the clutch 20 is fully disengaged. The mechanism 42 stops adjusting when the clutch is fully worn. At which time, the tab 106 contacts an end of slot 108 to prevent further rotation of the right cam ring 48.
As set forth above, the Spicer Clutch has previously only been able to be pre-set within a tolerance range of 0.100 inches. This range, however, is insufficient and there is a substantial need in the art for a method and/or apparatus that can improve the pre-setting accuracy of such self-adjusting clutches.